Silicon carbide (SiC) has characteristics in which a breakdown electric field is larger by a single digit, a band gap is three times larger, and thermal conductivity is about three times larger than silicon (Si). Accordingly, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, and the like. A SiC epitaxial wafer is manufactured by growing a SiC epitaxial layer serving as an active region of a SiC semiconductor device on a SiC single crystal wafer processed from bulk single crystal of SiC produced by a sublimation method or the like according to chemical vapor deposition (CVD). The foregoing SiC single crystal wafer is used as a substrate in which a SiC epitaxial layer is formed.
As a cause of deterioration in the quality of a SiC epitaxial layer, a defect with a triangular shape (hereinafter referred to as a “triangular defect”) is known. A triangular defect is formed in a direction in which the apex of a triangle and its opposite side (base) are lined up sequentially in a step-flow growth direction (Non Patent Literature 3). That is, the opposite side (base) of the triangular defect is disposed in a direction perpendicular to the <11-20> direction. A plurality of causes of the triangular defect can be considered. Examples of the causes include damage such as a polishing flaw remaining on the surface of a substrate (wafer) (Patent Literature 1), a 2-dimensional nucleus formed in a terrace during step-flow growth (Patent Literature 2), a different kind of polytype of crystal nucleus formed in an interface between a substrate and an epitaxial layer at the time of an oversaturated state of an early growth stage (Non Patent Literature 1), and a minute broken piece of a SiC film to be described below. The triangular defect grows as the SiC epitaxial layer grows. That is, the triangular defect grows so that its area is increased while a shape substantially similar to a triangle using its starting point as the apex of the triangle is maintained (see the schematic diagram of FIG. 2). Accordingly, the size of the starting point is larger as the triangular occurs in the earlier growth stage of the SiC epitaxial layer, and the depth of the starting point in the layer can be estimated from the size of the triangular defect.
In order to improve a yield at the time of mass production of the SiC epitaxial wafer, reduction in the triangular defects is indispensable and Patent Literature 1 and Patent Literature 2 have suggested countermeasures against the cause for the reduction in the triangular defects.
In addition to the foregoing triangular defect, a minute broken piece (hereinafter referred to as a “downfall”) of a SiC film falling on a SiC single crystal wafer or a SiC epitaxial layer is also a cause of deterioration in the quality of the SiC epitaxial layer. The downfall is peeled off from the SiC layer deposited on a sealing (top plate) disposed on the upper side of an apparatus so as to face the upper surface of a susceptor including a wafer replacing unit. This downfall can also be a starting point of the triangular defect.
Here, when the SiC epitaxial layer grows, it is necessary to heat the SiC single crystal wafer which is a substrate at a high temperature and maintain the temperature. A method of performing heating using a heating device disposed on the lower surface side of the susceptor and/or the upper surface side of the sealing is mainly used as a heating maintaining method, (see Patent Literature 3 and Non Patent Literatures 2 and 3). When the sealing is heated, a heating method of performing heating by high-frequency induction heating using an induction coil is generally used and a heating device formed of carbon suitable for the high-frequency induction heating is normally used.
While the SiC epitaxial layer is formed, SiC may be deposited not only on the SiC single crystal wafer but also on the sealing. When the layer is repeatedly formed, an amount of SiC deposited on the sealing also increases. Therefore, the problem of the downfall also becomes notable particularly in mass production.
In order to improve a yield in mass production of the SiC epitaxial wafer, reduction in the downfall is also indispensable. In order to reduce the downfall, Patent Literature 4 discloses a configuration in which a cover plate covering a wafer is disposed on a SiC single crystal wafer so that the downfall can be inhibited from falling on the SiC single crystal wafer or the SiC epitaxial layer.